Glow plugs have been used to help initiate combustion in diesel engines. At one time, glow plugs, if used at all, were included just to minimize cold starting problems. Other uses were limited by concerns about the operating life of the glow plugs. Glow plug life was improved by making them with durable ceramic material such as silicon nitride. However, such materials are subject to an ion migration characteristic that can also limit operating life. An option to increase lifetime and allow more frequent operation than just cold starting was recognized to be applying alternating current (AC) to the glow plugs, in contrast to direct current (DC) power sources, as disclosed in U.S. Pat. No. 5,724,932, Mar. 10, 1998, and U.S. Pat. No. 5,809,957, Sep. 22, 1998. The patents disclose glow plug systems with AC power sources that include an alternator dependent on engine operation, such as one driven by a hydraulic pump system operated from the engine power train.
The above mentioned patents also are representative of art relating to controllers for modifying power applied to glow plugs according to certain conditions throughout operation of the engine. The controllers can comprise programmable microprocessors utilizing sensors and electronic signal technology of a general nature like that of widely used engine control systems, sometimes referred to as engine control modules (ECMs).
By way of further background, various different diesel engine fuel systems are known. They include some in which fuel is directly injected into the engine cylinders, without premixing with air in a manifold. In some advanced systems, the fuel is directly injected at or near the end of the compression stroke at pressures up to a maximum that is in excess of 20,000 psi. One type of direct injection system, referred to as a hydraulically actuated electronic unit injection (HEUI) fuel system creates the needed pressure hydraulically by a high pressure oil pump driven by the engine, so upon starting the engine is cold-cranked to get the pump pressure to a proper level. General background on such systems is contained in an article by M. Osenga, Diesel Progress, August 1998, pp. 82, 84, and 86.
Another aspect of current diesel technology is the interest in a capability of operating on different fuels besides common diesel fuel. Different fuels have different combustion characteristics that have been addressed in various ways, such as those described in a paper by R. L. Miller, et al., titled "Development of a Heavy-Duty, Flexible Fuel (Methanol-Diesel) Engine System", ASME, ICE-Vol. 27-3, Book No. 1011C, 1996, pp. 47-55.